LGPL and DLLs

[Arnoud Engelfriet]

Kelly Anderson wrote:
> The LGPL says that you can use an LGPLed library in a commercial setting. 
> However, they also make this requirement that you have to be able to 
> re-link the LGPL program into the proprietary program. My [IANAL] 
> understanding of the LGPL's intent in the re-linking language is so that 
> you can replace the part of a program that is under LGPL with a newer 
> version, or your own version, without the proprietary company's permission. 
> I kind of get what they are doing, trying to make the program semi-open, so 
> that you can still change things that are part of the library.

That's my understanding of the LGPL as well. You have to enable
anyone who receives your program and the LGPL library to be able
to replace the library. That may mean supplying source or object
code for your program, for example if you need to statically link
the two. But it's the responsibility of the user to ensure that
the replacement library is interface-compatible - see 6(b)(2) LGPL.

> If you put the LGPL library code into a DLL, and give instructions on how 
> to construct that DLL (or the project already comes in DLL form in the 
> first place) then is this generally understood to fulfill the re-linking 
> requirements of the LGPL?

That's how I understand it. You still have to ship the source for
the version you use of course.

> Assuming that the DLL is a solution to the re-linking issue, is the 
> proprietary company then within it's rights to say, "If, however, you do 
> replace this DLL with another version, you've gone off the reservation, and 
> we can't provide technical support for you until you put a 'blessed' 
> version of the DLL back into your installation."

I don't see why that would be a problem. The LGPL library already
comes without any warranty, and commercial distributors are not
required to offer any warranty (although they may do so if they
want - LGPL 15).

> At the same time, it seems unwise for the open source community to refuse 
> the help they could get from commercial "moles" who are willing to work on 
> their software under the context of the LGPL, if they could  use it for 
> commercial purposes.

You can use LGPL software for commercial purposes, as long as you
provide source and allow recipients to replace the library with
an updated version. 

Arnoud

-- 
Arnoud Engelfriet, Dutch patent attorney - Speaking only for myself
Patents, copyright and IPR explained for techies: http://www.iusmentis.com/